1. Technical Field
The present invention relates to an optical lens, a method for designing the optical lens, and an apparatus for manufacturing the optical lens.
2. Background Art
International Publication WO97/19382 on a progressive multifocal lens used as a spectacle lens suitable for presbyopia correction or other vision correction describes that a progressive refractive surface having been provided on the object-side surface in related art is provided on the eyeball-side surface. This configuration allows the object-side surface to be a spherical surface having a fixed base curve, whereby no variation in magnification caused by a shape factor will occur, and the difference in magnification between the distance portion and the near portion can be reduced. In addition, any change in magnification in the progressive portion can be suppressed. The resultant progressive multifocal lens can therefore reduce image sway and distortion due to the difference in magnification and provide a comfortable field of view. International Publication WO97/19382 further describes that image sway and distortion can be reduced also in a progressive multifocal lens for astigmatism correction by combining a progressive refractive surface with a toric surface for astigmatism correction based on a combination formula to form the eyeball-side surface.
The multifocal spectacle lens described in International Publication WO97/19383 has viewing portions having different power factors, such as a distance portion and a near portion, and achieves predetermined addition power by configuring the object-side surface in such a way that the difference in average surface power between the distance portion and the near portion is mathematically smaller than the addition power and configuring the eyeball-side surface in such a way that average surface power of the distance portion and average surface power of the near portion are adjusted. The configuration described above not only allows the average surface power of the object-side surface to be so adjusted that the difference in magnification between the distance portion and the near portion decreases but also allows the difference in average surface power between the distance portion and the near portion of the object-side surface. The resultant multifocal lens can therefore reduce image sway and distortion due to the difference in magnification and provide a wide bright field of view where astigmatism is corrected and a comfortable field of view where image sway and other disadvantages are suppressed.
JP-A-2003-344813 describes provision of a double-sided aspheric progressive power lens that has a small amount of difference in image magnification between the distance portion and the near portion and provides excellent vision correction according to prescriptions and a wide effective field of view having a small amount of distortion in use of the lens. Specifically, JP-A-2003-344813 describes that horizontal surface power DHf and vertical surface power DVf of a first refractive surface, which is the object-side surface, in a distance power measurement position F1 and horizontal surface power DHn and vertical surface power DVn of the first refractive surface in a near power measurement position N1 satisfy DHf+DHn<DVf+DVn and DHn<DVn; surface astigmatism components in the positions F1 and N1 on the first refractive surface are canceled by those on the eyeball-side surface, which is a second refractive surface; and the first and second refractive surfaces as a whole provide distance power and addition power based on the prescriptions.
JP-A-2004-004436 describes provision of a progressive power lens that provides improved spectacle performance by reducing image distortion and blur inevitably produced by a typical progressive power lens. To this end, the double-sided progressive lens described in JP-A-2004-004436 has an object-side progressive surface and an eyeball-side progressive surface so shaped that the object-side surface has negative surface addition power and the distribution of average surface power of the object-side surface is similar to that of the eyeball-side surface.
Although the above and other technologies have improved the performance of a progressive power lens, some users still cannot adapt to the characteristics of a progressive power lens, particularly an image sway characteristic, and further improvement is therefore required.